Project Summary Lung cancer is the leading cause of cancer death in the United States, with African Americans (AAs) suffering a higher lung cancer incidence than any other ethnic or racial group, for reasons that are poorly understood. Recent studies have shown that the lungs are inhabited by communities of diverse types of bacteria and that bacterial infection in the lungs has been associated with lung cancer risk. Recent studies have also shown that the oral microbiome is the primary source of bacterial microbiota in the lungs and that the bacterial communities of the lungs overlap those found in the mouth. We found in our pilot study that multiple bacterial taxa in mouth rinse samples were associated with lung cancer risk. We hypothesize that (1) oral microbiomes may play a role in the etiology of lung cancer, (2) oral bacteria may interact with cigarette smoking and chronic lung diseases to influence lung cancer risk, and (3) the oral microbiome of AAs may differ from that of European Americans (EAs) in ways that could lead to a high incidence of lung cancer in AAs. To test these hypotheses, we will use already collected data and stored biospecimens from the Southern Community Cohort Study (SCCS) and Black Women's Health Study (BWHS). Mouth rinse samples were collected from approximately 39,000 SCCS participants and 28,000 BWHS participants using a similar collection method. In the proposed study, we will conduct a nested case-control study of lung cancer, with 800 incident cases (600 AAs and 200 EAs) and 1,000 matched controls (600 AAs and 400 EAs), using pre- diagnostic mouth rinse samples. We will perform whole metagenome shotgun sequencing and use advanced biostatistics and bioinformatics techniques to investigate oral microbial composition (bacterial species/strains abundance and diversity) and functional capabilities (bacterial genes/pathways abundance and diversity) for their associations with lung cancer risk (Aim 1). We will evaluate the possible interaction of oral microbial communities with other risk factors in relation to lung cancer risk (Aim 2). We will further evaluate whether the oral microbiome and lung cancer association differs between AAs and EAs and whether African ancestry modifies the microbiome-lung cancer association (Aim 3). Finally, we will perform in vitro studies to evaluate potential function of identified bacteria (Aim 4). The proposed study is highly innovative, as there are no published studies on the association between the oral microbiome and lung cancer risk. The exceptional resources of the SCCS and BWHS, coupled with state-of-the-art whole metagenome shotgun sequencing and bioinformatics technologies, provide an unprecedented opportunity to evaluate the role of the oral microbiome in lung cancer risk. Results from our proposed study will increase understanding of the pathophysiological effects of microbiomes on the etiology of lung cancer and could provide useful information for preventive interventions as well as providing new information to ameliorate disparities in lung cancer.